Earthquake analysis and response of concrete arch dams

Reliable analytical procedures to predict the earthquake response of arch dams are essential to design dams to be earthquake resistant or to evaluate the earthquake safety of existing dams. The objectives of this study are: (a) to develop an effective and computationally efficient procedure for analyzing the response of concrete arch dams to earthquake ground motion, including the effects of dam-foundation rock interaction with inertia and damping of the foundation rock considered, dam-water interaction, and reservoir boundary absorption; (b) to identify the limitations of "standard" analysis which considers the flexibility of the foundation rock but ignores its inertia and damping--material and radiation--effects; and (c) to study how the various interaction mechanisms separately or jointly affect the earthquake response of arch dams. This investigation emphasizes the effects of dam-foundation rock interaction compared to dam-water interaction that has already been studied extensively.; An earlier analytical procedure to evaluate the earthquake response of arch dams considering the various effects of dam-water interaction is extended to include the effects of dam-foundation rock interaction with inertia and damping of the foundation rock considered. In this extended procedure, the foundation impedance matrix is computed by a direct boundary element method. The computational efficiency of the extended analytical procedure is improved profoundly by developing more efficient methods for evaluating the foundation impedance coefficients.; Utilizing the resulting analytical procedure, the response of a selected arch dam to harmonic and earthquake ground motions is computed and studied for a wide range of the important parameters characterizing the properties of the dam, foundation rock, impounded water and reservoir boundary materials. It is shown that: (a) dam-foundation rock interaction reduces the amplitude and resonant frequencies, and widens the frequency bandwidth of the fundamental and higher resonant peaks in the frequency response function; (b) dam-foundation rock interaction generally increases the earthquake response of the dam; (c) dam-foundation rock interaction should be considered in the earthquake analysis of arch dams because the commonly used "standard" analysis, which considers only the foundation flexibility but ignores other effects of dam-foundation rock interaction, significantly overestimates the earthquake-induced stresses in arch dams; and (d) dam-foundation rock interaction, dam-water interaction, and reservoir boundary absorption may significantly affect the earthquake response of arch dams; therefore, these effects should be included in the design of new arch dams and in the seismic safety evaluation of existing dams.